Communication devices such as User Equipments (UE) are also known as e.g. wireless terminals, mobile terminals, mobile stations or mobile devices. Communication devices are enabled to communicate or operate wirelessly in a heterogeneous wireless communication environment comprising multiple wireless communication networks. The heterogeneous wireless communication environment may comprise cellular communications networks complying with the 3rd Generation Partnership Project (3GPP) standard, e.g. Second/Third Generation (2G/3G) network, 3G/4G Long Term Evolution (LTE) network, Worldwide interoperability for Microwave Access (WiMAX) network etc., satellite positioning systems, e.g. Global navigation satellite systems (GNSS) and Global Positioning System (GPS) etc., wireless local networks, such as Wireless Local Area Networks (WLAN) or Wi-Fi/Wi-Fi Direct networks etc. as well as other short-range wireless communication networks using various technology standards, e.g. Near Field Communication (NFC), Bluetooth or Bluetooth Low Energy (BLE), Radio Frequency Identification (RFID) and 60 GHz and Ultra-wideband (UWB) standards etc.
Communication devices may further be referred to as mobile telephones, cellular telephones, smart phones, laptops, tablet computers or phablets with wireless communication capability, just to mention some further examples. The communication device in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data via an access point with another entity, such as another communication device or a server in the wireless communication environment.
Mobile Positioning for estimating the position of a communication device uses a number of different techniques that use wireless signals and process them into a location or position estimation. Typical information used for positioning includes GPS signals, Received Signal Strength Indicator (RSSI), single trip or round-trip Time Of Arrival (TOA), Time Difference Of Arrival (TDOA), Angle Of Arrival (AOA), and Doppler shift etc. These techniques are complementary since some methods are more suited for indoor settings while others are more reliable in outdoor settings.
There are however a number of sources of errors in wireless positioning methods. One of the sources of errors is multipath propagation, which occurs when a signal takes different paths when propagating from a source to a destination receiver. While the signal is traveling, objects get in the way and cause the signal to bounce in different directions before getting to the receiver. As a result, some of the signals are delayed and travel longer paths to the receiver. In other instances there is no direct line of sight because an object is completely blocking and any received signals occur only due to multipath propagation. A Radio Frequency (RF) signal amplitude is also greatly affected by metal objects, reflective surfaces, multipath, dead-spots, noise and interference. These effects cause errors in GPS data, RSSI, AOA, TOA, TDOA and Doppler shift. For example, the longer multipath propagations also result in smaller signal amplitude indicators such as RSSI, as well as incorrect values for AOA and Doppler shifts. Other sources of positioning errors are clock drift, synchronization errors, and measurement errors. These errors cause incorrect mobile position calculations for traditional location techniques.
Indoor Mobile Positioning has gained increasing tractions in recent years due to the widely deployed smart phones and indoor mobile networks such as small cells, Wi-Fi, BLE or RFID which provide improved infrastructures for assisting and signal processing of Mobile Positioning. As discussed above, GPS and GNSS are generally not suitable to establish indoor locations, since microwaves will be attenuated and scattered by roofs, walls and other objects which causes the GPS and GNSS signals are too weak to use. Furthermore cell-based wireless networks, e.g. cellular communications networks are optimal for communications but not positioning.
U.S. Pat. No. 8,700,060 has provided a solution based on location databases which associates the location of an Access Point (AP) to its Identity (ID), and a UE may calculate its position from the locations of the APs stored in the location database and reachable by the UE. One of the problems of this solution is to build up databases using the locations of the UEs gained from GPS, which is in general not feasible for indoor environment for the reason described above. Further there is a large amount of data to be created, transferred via the network, processed and stored in the location database server as well as in the local location database in the UE, and keep them updated. Moreover considerable number of APs should be in the reach of the UE simultaneously and the locations of the APs are usually not the physical locations of the APs or the UE, but the statistical average locations of other UEs reported to the location database. As a result, the accuracy of the calculated position of the UE is unpredictable.
US2013029685 has developed a solution which employees localized wireless reference devices for re-calibrating a position of a mobile terminal. The solution uses position assistance information from the reference devices to replace the computed position at a reference point, and then to modify parameters such as clocks of the APs or weights of positions computed from measured RSS values to make the computed position match to the known one at the reference point. However the measured RSS values are dynamic and depend heavily on the surrounding radio environment, and thus the positions computed directly from the measured RSS values are unstable and unreliable. Consequently the efforts to perform a posteriori processes based on such inputs would hardly lead to convergent and accurate results.